1. Field of the Invention
The present invention relates to a driving method for a CCD image sensor and an imaging method with use of the CCD image sensor, and more particularly to a driving method for a CCD image sensor and an imaging method in which noise correction is effectively performed.
2. Description Related to the Prior Art
A CCD image sensor is well known as a solid-state imaging device included in a digital camera, a camera phone or the like. The CCD image sensor comprises photoelectric conversion elements (photodiodes) arranged in a two-dimensional matrix to convert entering light into signal charge based on the amount of light and to accumulate the signal charge, a plurality of vertical CCDs provided for respective vertical lines of the photoelectric conversion elements to vertically transfer the signal charge, a horizontal CCD to horizontally transfer the signal charge received from the vertical CCDs, and an output circuit to convert the signal charge received from the horizontal CCD into image signal based on the charge quantity and to output the image signal.
In the CCD image sensor, a specific noise so-called smear is caused. The smear is resulted from undesired electric charge getting into the vertical CCD. The smear works as a dark-current noise (an offset to an appropriate black level) which changes a black level of whole of the obtained image. To solve this problem, Japanese patent laid-open publication 2003-264736 discloses a method to obtain correction data (the dark-current noise) for correcting the black level.
However, in the method of Japanese patent laid-open publication 2003-264736, the data obtaining correction is performed separately from the image capturing operation, and therefore extra time is needed. Accordingly, a time lag is caused in image capturing. Although the time lag does not affect a long time exposure, it becomes a problem in a continuous shooting and so on.